If Only You Knew
by romeokijai
Summary: Amy Santiago meets an old college rival and unintentionally lies about her current relationship status. What happens when said rival insists on meeting the boyfriend that Santiago doesn't actually have? Peraltiago multi-chapter fic. Fake boyfriend trope. Rated M for language and possible sexual situations (don't worry, I'll keep it tasteful!). I live for feedback, so please R&R!
1. Chapter 1

**AUTHOR'S NOTE: Welcome to my very first Brooklyn Nine-Nine fic! I've been writing fan fiction for quite a while (for other fandoms and on platforms outside of ), but I finally decided to try my hand at B99. I'm a huge Jake x Amy (Peraltiago) fan, and this is my first attempt at capturing their magic. I live for feedback, so please leave a review! Good or bad...I'd like to know how I'm doing. I'm not sure how long this will be…probably about 5 chapters. But time will tell, I s'pose. For the purposes of this story, please assume that Jake hasn't confessed his feelings and that Amy and Teddy never happened.**

**As always, I don't own anything…blah, blah blah. Rating this 'M' just in case, but I expect this to hover somewhere in between 'T' and 'M'. Thanks for reading! **

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><p><strong>CHAPTER ONE: Amy Santiago's Day Off<strong>

"C'mon, please?" Amy begged. Her words came out in utter desperation. She still couldn't believe this was actually happening. Had the world really come to…well, _this_?

Even as she begged, she still couldn't believe she was asking _him_, of all people, to do _this_ for her. But, as they say: _desperate times call for desperate measures. _

Of course, she could've just called the whole thing off and told her friend—err…nemesis—the truth. But, as usual, her pride and competitive nature refused to let her do so.

Her eyes anxiously searched his, and she couldn't help but scowl at him in the process. _Why isn't he saying anything?!_ She watched as he pretended to shiver.

"Oh, Santiago…" he finally said, his voice suddenly low and sultry. "I love it when you beg. It makes my insides all tingly."

"Ew. Shut up," she groaned. She picked up a pen and attempted to throw it at him, but he easily dodged it and then cackled when it hit Scully instead. "Ugh…sorry, Scully."

"Huh?" Scully shrugged, oblivious to what had just had happened as he shuffled past their desks, coffee and a large jelly-filled donut in hand.

Amy rolled her eyes and brought her attention back to her partner. "So, what's your answer? Will you do it, or not?"

Jake thoughtfully tapped the dimple on his chin. "_If_ I agree…what exactly am I gonna get out of it?"

"I don't know." She frowned. "What do you want?"

But as soon as the question had left her lips, she found herself remorsefully grimacing. Asking Jake Peralta what he wanted was an extremely dangerous course of action. And based on the mischievously arrogant smirk that had erupted on his face, Amy was now certain she'd just dug her own grave.

"Whatever it is, it has to be reasonable," she quickly added.

"Define reasonable." He continued to grin.

"It has to be work-related."

"Define work-related."

"Ugh. You know what? Forget it. It was stupid of me to even ask you. I'll just find someone else."

"Ha! Like that's even an option!"

"Excuse me!" She glowered. "What the hell is that supposed to mean?"

Jake leaned back in his chair and folded his arms over his chest. "Well, aside from the _obvious_ fact that there's nobody as devilishly handsome and charming as me, reality is, you wouldn't be able to find another guy to do it even if you tried. You barely know any dudes, let alone attractive, single ones who would agree to this kind of torture."

"I do too know guys! Plenty of them…who are far more polite and more mature than you." Amy arrogantly pouted her lips.

"Yeah? Like who? And you can't say Holt, because a) he doesn't swing for your team, 2) you wouldn't have the guts to ask him even if he did or were single, and tres) it'd probably end up being some sort of workplace violation anyway."

Amy just frowned and blinked while racking her brain. Did she really not know any other suitable guys? Was Peralta genuinely her only option?

Jake's grin grew more confident. "I rest my case."

"Fine, whatever. Just tell me what I have to do to get you to comply."

"Muwahaha…" He rubbed his hands together in a plotting and sinister fashion. "There are _so_ many possibilities."

A throaty whine struggled past Amy's lips. "Can't we just agree that the weekend will be torture enough for me, and that itself can be my punishment? And you can tease me about it for as long we both live?"

"Oh, sweet Amy." Jake sniffled melodramatically. "I would _never_ make it that easy."

She exhaled sharply, her impatience escalating by the second. "Well, then hurry up and tell me your stupid terms so we can call it a deal already. I can't sit here all day and discuss this with you. I have a lot of work to do today."

"Fine," he sighed, this time showing at least an inkling of seriousness. "If I do this, here's the deal."

Amy sucked in a deep breath and held it. This was going to be painful. She was sure of it.

"You have to pull a serious prank on Holt – which_ I_ will plot out in infinitesimal detail; _and_, you have to intentionally get caught, thus relinquishing your whole Santiago-style, ass-kissing persona that you've developed with him."

Amy's eyes widened in horror. She could feel the color draining from her face. "WHAT?! I can't…I'm not—I'm not doing that! _Peralta_!"

"What?" He snickered, thoroughly amused with himself and with her reaction. "You said it had to be work-related."

"I was talking about…like doing your paperwork for you or something. But—but now we're talking about pranking the _Captain_!"

"Uh…yeah! Exactly! This will be _way_ more entertaining."

She couldn't believe this was happening. And yet, she wasn't completely surprised, either. _Ugh. Damn him!_

"No. It's too risky. I won't do it." Amy shook her head.

Jake sighed and mimicked her actions. "You disappoint me, Santiago. You _deeply_ disappoint me."

"Can't you come up with some other form of payment? Please?" She begged. There had to be another way.

"Nope. Those are my terms. Either take it or leave it."

Amy's chest was beginning to tighten with remorse and frustration. She knew she'd completely hate herself for this decision later, but again: what else was she supposed to do?

So, with a defeated scowl strewn across her face, she used every bit of strength she could possibly muster and reached her hand across the desk.

"Wait," Jake replied in surprise. "You mean, you'll do it?"

Amy's face bitterly scrunched up. "Just shake my hand before I change my mind, Peralta."

"Yes!" Jake immediately hopped to his feet, pumped his fist, and grabbed her hand with both of his. "You've got yourself a deal, Santiago! Say hello to your new fake boyfriend!"

_Great._ Amy's eyebrows tightened into a frown while Jake offered her his best Blue Steel face.

**_-_****24 Hours Earlier-**

Ah, the sweet joys of a day off after a long and grueling solve! After her outstanding work as the primary on a recent murder, Captain Holt had given Amy an unexpected but much-needed day off, and she couldn't be more excited. She'd been working several double shifts lately, so this sudden break was a much-welcomed reward.

Plus, it meant she'd get a bit of a breather from her annoying partner.

Jake was a great detective, no doubt – one of the best in the 99th precinct, in fact (although it pained Amy to admit that, and she would never acknowledge it in front of Jake). But his maturity level was that of fourteen-year-old boy. And, for whatever reason, since the day they'd been partnered together, he'd made it his life's mission to find every possible way known to mankind to irritate Amy, and, to her misfortune, had developed a pretty high success rate.

But today, there would be no Jake, no pranks, no perps, and no annoyingly dramatic civilians to deal with at the precinct. Amy could finally have a moment of peace all to herself.

She started her day by sleeping in, and then spent a couple hours lounging around her apartment in her pajamas. By the time early afternoon rolled around, she was off to her favorite spa and nail salon for a mani/pedi and massage. A good pampering was exactly what she needed today.

"Detective Santiago!" The owner of the spa – a petite, middle-aged Asian woman – lit up when Amy walked in. "Nice to see you today. It's been a while."

"Nice to see you, too, Rose. And, yes, it has." Amy smiled.

"Very busy working these days?"

Amy sighed and nodded. "Extremely."

"Well, I'm glad you're here. It's good to relax. What are we doing today?"

"The usual. And if you don't mind, I'd like to start with the massage. My back and shoulders have all sorts of knots in them."

"Sure, go ahead and get ready in Room 2," Rose instructed.

After a full body massage, it was on to the pedicure and manicure. Amy eagerly settled into the large leather pedicure chair and sighed in relief as her toes hit the warm, sudsy water. While she soaked, she pulled out her Kindle and started browsing her collection of e-books. She eventually settled on _Sense and Sensibility_, even though she'd read it and most of Jane Austen's other novels about a hundred times already.

"Amy? Amy Santiago?" A voice interrupted her just as soon as she began to focus on her reading. _Ugh. Now what? _

When she reluctantly looked up, she felt her face and body stiffen. Sitting in the pedicure chair directly next to her was none other than Lindsey Nelson, Amy's biggest college rival.

"Hi…" Amy forced her lips into a smile. "Wow…long time no see."

"I'll say," Lindsey agreed a bit too dramatically.

Amy watched with mild irritation as Lindsey flipped her long, perfectly curled blonde hair from one side to the other, the thick locks cascading from her right shoulder to her left and somehow falling into perfect place.

_What is this, a L'Oreal shampoo commercial?!_

But that's just how Lindsey was: always picture perfect. And she wasn't just one of those outwardly pretty but ultimately ditzy blondes, either. In fact, if it hadn't been for Lindsey Nelsen, Amy would have earned the title of Class Valedictorian when she graduated from NYU in 2004. But Lindsey had surpassed her by a measly 0.015 GPA difference, thus stealing the very title that Amy had spent all four years of college trying to acquire.

Needless to say, Lindsey and Amy didn't keep in touch after graduation. Lindsey had gone on to pursue graduate school at Oxford University in England while Amy went straight into the police academy.

But now Lindsey was obviously back…for God knows what reason.

"So…what have you been up to? And what are you doing back in New York?" Amy asked, trying her best not to sound annoyed or fake.

"Oh, well, you know…I extended my studies at Oxford and ended up earning my PhD there as well. And then, immediately upon graduation, they offered me a teaching residency. But I turned it down. I wanted to explore other options first…just in case something better came along."

Amy resisted the urge to roll her eyes. "Oh…well, good for you, Lindsey. I hope you find what you're looking for."

"Yeah." Lindsey smiled. "So what about you? Did you ever make it into the police force?"

"I did, indeed." This time, Amy tried not to sound arrogant…or at least, not _too_ arrogant. She was, after all, quite proud of her vocational accomplishments. "Right now, I'm working as a detective in the 99th precinct, and I plan to work my way up to Captain…or, who knows? Maybe even Commissioner, someday."

Lindsey nodded, but her face looked unapologetically unimpressed. "I'm actually surprised you're still a detective…in the 99th precinct, no less. I mean, isn't that one of the lowest performing precincts around? I thought I read somewhere that you guys have had the lowest number of arrests three years in a row?"

Amy could feel her face heating up; she was sure she was blushing. "Well, that's only because we've had a lot of administrative transitions recently. For example, we got a new Captain last year, and, as one might expect, it's taken him a little bit of time to really learn the systems and implement the necessary changes. But crime in our area has actually decreased by 3 percent since Captain Holt took over the precinct."

Lindsey nodded again, still unimpressed and now also uninterested. She began leafing through the magazine on her lap.

Amy clenched her jaw and tried to take a deep breath. How dare Lindsey come in and tell her that she and her colleagues weren't good at their jobs! What did Lindsey know, anyway? She was just one of those pretentious academic types; she didn't get to experience the day-to-day thrill of helping real people, like Amy did.

Perhaps it was time to change the subject. Not that Amy had any genuine interest in continuing a conversation with her nemesis in the first place, but she certainly wasn't going to let Lindsey have the last word…not to mention, the last word being an insult to Amy's profession and achievements.

"So what else have you been up to since you've been back in New York?"

"Actually, I'm getting married. This weekend, in fact."

"Oh!" Amy said, surprised and also relieved to change the subject. "Well, congratulations."

"Thank you!" Lindsey beamed.

"Although, I have to admit, I figured you'd have married a while ago." _Ha! Burn!_

"Well, Jason, my fiancé, and I really wanted to finish our academic pursuits before we tied the knot."

"I see. So what does Jason do?"

"He's a professor of Medieval History and Literature at Columbia."

"Of course. Well…sounds like he's great for you." Amy hoped that the conversation would end there, on a cordial note, so she could get back to her reading while one of Rose's assistants began scrubbing her feet.

"And what about you?"

_Shit. Well, of course that question was going to come up._ "Hmm?" Amy pretended she didn't understand.

"Are you with someone?" Lindsey asked. "I mean, I would imagine it's really difficult to find someone who's willing to settle down with a cop, no?"

Amy dug her fingernails into the leathery arms of her chair. She was about to respond, but Lindsey continued.

"In fact, I think I recently read a survey about female NYPD officers and how they're marrying later and later – or just staying single all together, because it's such a challenge to find someone who's willing to deal with the demanding and unpredictable lifestyle of their partner."

"Well, that's not the case for me. I'm with someone," Amy blurted out.

_…wait, what?!_

Now Lindsey looked genuinely intrigued. "Oh! Well, that's wonderful, Ames! Good for you, truly."

_Oh my god, what have I done?! _Amy hoped with everything in her that her facial expression wasn't betraying her sudden and unexpected lie. "Thanks. We're very happy. He's incredible."

"That's great. So what does he do?" Lindsey paused and chuckled. "Or…she? I'm in no position to judge."

"He's also a detective. In my precinct."

_WHAT?! WHAT. ARE. YOU. SAYING?!_

"His name is Jake."

_FUCKING HELL, AMY! SHUT YOUR MOUTH!_

"Aww…well, good for you, Sweetie. I'm happy you found someone." Lindsey looked satisfied and, to Amy's slight and only momentary relief, oblivious to the lie.

"Thanks," Amy muttered.

Her heart was now racing, and she really wished she could get up and run out of the salon. But, given the fact that her toes were smack dab in the middle of being painted, that wasn't exactly a viable option.

Suddenly, Lindsey perked up in her seat. "Hey…this might sound crazy…."

_Oh god. Is she going to ask what I think she's going to ask? Please, god…no! _

"…would you and Jake like to come to the wedding? I'd love to meet him."

_Aaaand, there it is. _

_Shit. _

Once again, Amy forced herself to smile. "Um…well, I dunno. You said it's this weekend, right? I'm pretty sure Jake and I are both working." _Lies._ "Some community development seminar, or something; our Captain would be extremely disappointed if we weren't there to help out." _Lies on top of lies._

"Aww, come on. I'm sure he could make an exception if you told him it was for an old friend."

_Old friend? Now we're friends?_ "Even if…I mean, isn't it too late to be adding people to your guest list?"

Lindsey waved a nonchalant hand at her. "Oh, that's no biggie. It's my wedding, isn't it? And since the wedding is up in Martha's Vineyard, not everyone we invited will be attending, anyway. We still have plenty of space on the RSVP list."

"Are you sure?" Amy questioned. _Please change your mind, please change your mind, please change your mind…._

"Positive," Lindsey affirmed.

_Damnit. _

"Well, the Captain is extremely strict and takes these seminars very seriously." _Okay, so at least that one wasn't a lie. Sort of. _"And I'd really hate to disappoint him."

Lindsey was about to say something, but then she stopped and quietly giggled. "Amy Santiago, you haven't changed at all. Always putting your studies…or in this case, your job…in front of everything else. You need to learn to live a little."

Both the giggle and the proceeding comments rubbed Amy the wrong way. "I…live." She tried her best to play it cool. And clearly failed. Which left her nothing but one option: "Actually, you know what? I'm sure I could get my colleagues to cover the seminar for me or something. It shouldn't be a problem."

_Yup. Not a problem at all. I'm sure Rosa or Charles would be happy to cover an IMAGINARY SEMINAR._

Lindsey's blue eyes quickly lit up. "Great! Oh, I'm so glad!" She grabbed her purse and whipped out an invitation. "You're going to love the little hotel at Martha's Vineyard. It's at this amazing beach resort with glorious waterfront views. And the rooms are just exquisite."

_Smile. Smile, you idiot!_ "That sounds lovely."

"It truly is. And I can't wait to introduce you to Jason. And, of course, to meet Jake."

Amy felt sick to her stomach as she stared at the invite. She suddenly had a horrible flashback of Captain Holt's birthday party and the way Jake had made a complete fool of himself in front of Captain Holt, Kevin, and their other guests. Then again, Amy couldn't completely blame him; her own behavior that night hadn't exactly been classy or crowd-pleasing, either.

"I can't wait for you to meet him, as well." _Oh. MY. GOD. Why are you still talking?!_

"It will be great," Lindsey agreed. "I'm sure Jake's a catch."

_If only you knew…._


	2. Chapter 2

**Thank you so much for great response to this fic! I appreciate the reviews very much. Please keep them coming! :)**

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><p><strong>CHAPTER TWO: Friday Morning Shenanigans<strong>

"Good morning, my beautiful little love nugget!" Jake announced all too cheerily as he entered the precinct office on Friday morning. His eyes, which were fixed on Amy, were a bit crazed and his smile, mischievously wide.

"You're late, Peralta," Captain Holt stated in his typical monotone.

"Yes, Captain, I am," Jake agreed. "And for that, I apologize. But you see, I decided to stop and get my pretend _girlfriend_ over there—" he pointed at Amy, "a special breakfast, and I might have underestimated the line at the café."

"Unsurprising," Holt answered curtly and walked into his office without further discussion.

Amy, who was already at her desk, wanted to crawl underneath it and die. It was bad enough that Jake was making her prank Captain Holt; but he obviously wasn't going to make the rest of their deal any easier, either. She genuinely couldn't figure out which was worse: having to prank her boss and mentor or having to spend a weekend with Peralta as her fake boyfriend.

She watched in dismay as Jake placed a 16-oz coffee and a paper pastry bag in front of her and then settled into his chair, smile still intact.

_Well, at least he brought me breakfast._ Maybe this pretend relationship would end up having some benefits after all. She reached for the bag, hoping he'd brought her a blueberry muffin or a cheese danish – her two favorite breakfast pastries.

"Peralta!" She growled, pulling out the half-eaten muffin. "What the hell?!"

"What? I got hungry on the way here." He shrugged.

Amy rolled her eyes and sighed.

The morning went by fairly quickly, and, despite Jake's constant shenanigans, Amy was able to focus and accomplish quite a bit of work. Normally, that kind of productivity would have given her a huge amount of satisfaction; but today, not so much. She couldn't even begin to enjoy it because she knew that as soon as she was done with everything, her weekend from Hell – that she'd completely brought upon herself – would officially have to begin.

"Captain? May I come in?" She asked, tapping gently on Holt's office door.

As usual, Holt was behind his desk, looking as stoic as ever. He motioned for her to enter.

"Here's that report you wanted." Amy handed him the document. "Are you sure you don't need me to stick around and do anything more today?"

Holt barely – just _barely _– quirked up an eyebrow. Or maybe he didn't. Amy wasn't quite sure. No one ever was.

"Didn't you specifically request half a day off so you and Detective Peralta could leave for your friend's wedding in Martha's Vineyard?" He asked.

"College rival," Amy corrected, then frowned and shook her head. "Lindsey and I aren't…weren't…exactly friends…and to be honest, I don't even want to go to."

"So then…why did you agree to attend?"

She sighed heavily. "I don't know! It just sort of happened. My competitiveness is a curse. Which is why, sir…if you need me to stay for the rest of the day – or, you know, to cover for the weekend crew or anything like that, I'd be happy to do it."

"No, that won't be necessary."

"Are you sure? Surely, I could find some paperwork to catch up on or something."

"Detective Santiago, your paperwork is always in on time and in impeccable order."

Amy grinned. "Thank you, sir."

"Therefore, it will not be necessary for you to put in overtime this weekend. Enjoy the wedding and your weekend. Dismissed." And with that, Holt focused his attention on the report Santiago had just handed him.

Her grin disappeared and her shoulders slumped in defeat. "Thank you, sir," she replied, dragging herself out of his office.

She found Jake sitting on the edge of his desk, looking around, as if in search for something.

"What?" Amy asked. "What are you looking for?"

"Oh, I was just looking for the old lady who belongs to this luggage set." He pointed to the brown and pink floral tapestry suitcase and matching tote bag that were placed beside Amy's desk.

She rolled her eyes. "These are mine, you idiot. They're vintage."

"Shocking!" Peralta snickered. "So, you ready to go?"

"Ready as I'll ever be," she muttered. Then she had an idea. "Hey, since you're my boyfriend for the weekend, be a gentleman and carry my bags for me, please?"

"Fat chance, Santiago. Besides, I have my own luggage to carry."

Amy watched with raised eyebrows as Jake pulled out a large _Toy Story_ Buzz Lightyear rolling backpack and smugly placed it on his desk.

"Seriously? _That's _your luggage?" She folded her arms in front of her.

"Um…duh! Besides, are you really in a position to be judging?" He nodded toward her suitcase and tote again.

"Ugh. You're hopeless." She grabbed her bags. "Let's get out of here. The sooner this weekend starts, the sooner it'll be over."

"Have fun, you two lil' love bugs!" Gina teasingly hollered after them, which caused the others, like Charles, Rosa, and Terry, to cheer. "Don't come back a real couple!"

"Like _that _will ever happen!" Amy quipped as she and Jake headed for the elevator.

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><p><strong>Sorry this chapter's a bit short. More coming soon! Stay tuned! Please leave reviews. :)<strong>


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